Wireless telecommunications apparatus and methods

ABSTRACT

A method of operating a terminal device in a wireless telecommunications network comprising the terminal device and a base station. The wireless telecommunications network supports a random access procedure comprising an exchange of random access procedure messages between the terminal device and the base station. At least one of the random access procedure messages is a variable size uplink message. The method comprises: receiving from the base station an instruction to perform the random access procedure, wherein the instruction to perform the random access procedure comprises an indication of a message size to be used by the terminal device for the variable size uplink message during the random access procedure: and performing the random access procedure by exchanging random access procedure messages with the base station, including transmitting the uplink message of variable size with a size corresponding to the indicated message size received from the base station.

BACKGROUND Field

The present disclosure relates to wireless telecommunications apparatusand methods.

Description of Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Third and fourth generation mobile telecommunication systems, such asthose based on the 3GPP defined UMTS and Long Term Evolution (LTE)architectures, are able to support more sophisticated services thansimple voice and messaging services offered by previous generations ofmobile telecommunication systems.

For example, with the improved radio interface and enhanced data ratesprovided by LTE systems, a user is able to enjoy high data rateapplications such as mobile video streaming and mobile videoconferencing that would previously only have been available via a fixedline data connection. The demand to deploy third and fourth generationnetworks is therefore strong and the coverage areas for these networksis expected to increase rapidly.

The anticipated widespread deployment of third and fourth generationnetworks has led to the parallel development of devices and applicationswhich, rather than taking advantage of the high data rates available,instead take advantage of the robust radio interface and increasingubiquity of the coverage area. Examples include so-called machine typecommunication (MTC) applications, which are typified by semi-autonomousor autonomous wireless communication devices (i.e. MTC devices)communicating small amounts of data on a relatively infrequent basis.Further information on characteristics of MTC-type devices can be found,for example, in the corresponding standards, such as ETSI TS 122 368V12.4.0 (2014 October)/3GPP TS 22.368 version 12.4.0 Release 12 [1].Some typical characteristics of MTC type terminal devices/MTC type datamight include, for example, characteristics such as low mobility, highdelay tolerance, small data transmissions, a level of predictability fortraffic usage and timing (i.e. traffic profile), relatively infrequenttransmissions and group-based features, policing and addressing.

A current technical area of interest to those working in the field ofwireless and mobile communications is known as “The Internet of Things”,or IoT for short. The 3GPP has proposed to develop technologies forsupporting narrow band (NB)-IoT using an LTE/4G wireless accessinterface and wireless infrastructure. Such IoT devices are expected tooften be low complexity and inexpensive devices requiring infrequentcommunication of relatively low bandwidth data (e.g. MTC devices).

The increasing use of different types of terminal devices associatedwith different traffic profiles gives rise to new considerations forefficiently handling signalling associated with such devices. This isbecause approaches for efficiently handling transmissions associatedwith one traffic profile, e.g. frequent transmissions of large volumesof data, may be different from approaches for efficiently handlingtransmissions associated with another traffic profile, e.g. infrequenttransmissions of small amounts of data.

In view of this there is a need for methods and apparatus that can helpprovide for increased flexibility in respect of the signalling used fordata transmissions in wireless telecommunications systems.

SUMMARY

The present disclosure can help address or mitigate at least some of theissues discussed above.

Respective aspects and features of the present disclosure are defined inthe appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, but are notrestrictive, of the present technology. The described embodiments,together with further advantages, will be best understood by referenceto the following detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings wherein likereference numerals designate identical or corresponding parts throughoutthe several views, and wherein:

FIG. 1 schematically represents some aspects of a LTE-type wirelesstelecommunication network which may be configured to operate inaccordance with certain embodiments of the present disclosure:

FIG. 2 schematically represents steps in a random access procedure in awireless telecommunication network;

FIG. 3 schematically represents some aspects of a wirelesstelecommunications network configured to operate in accordance withcertain embodiments of the present disclosure; and

FIG. 4 is a ladder signalling diagram schematically representing someoperating aspects of terminal devices and base stations associated withrandom access procedures in accordance with certain embodiments of thepresent disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 provides a schematic diagram illustrating some basicfunctionality of a mobile telecommunications network/system 100operating in accordance with LTE principles and which may implementembodiments of the disclosure as described further below. Variouselements of FIG. 1 and their respective modes of operation arewell-known and defined in the relevant standards administered by the3GPP (RTM) body, and also described in many books on the subject, forexample, Holma H. and Toskala A [2]. It will be appreciated thatoperational aspects of the telecommunications network which are notspecifically described below may be implemented in accordance with anyknown techniques, for example according to the relevant standards.

The network 100 includes a plurality of base stations 101 connected to acore network 102. Each base station provides a coverage area 103 (i.e. acell) within which data can be communicated to and from terminal devices104. Data is transmitted from base stations 101 to terminal devices 104within their respective coverage areas 103 via a radio downlink. Data istransmitted from terminal devices 104 to the base stations 101 via aradio uplink. The core network 102 routes data to and from the terminaldevices 104 via the respective base stations 101 and provides functionssuch as authentication, mobility management, charging and so on.Terminal devices may also be referred to as mobile stations, userequipment (UE), user terminal, mobile radio, communications device, andso forth. Base stations, which are an example of network infrastructureequipment, may also be referred to as transceiverstations/nodeBs/e-nodeBs, and so forth.

In wireless telecommunications networks, such as LTE type networks,there are different Radio Resource Control (RRC) modes for terminaldevices. For example, it is common to support an RRC idle mode(RRC_IDLE) and an RRC connected mode (RRC_CONNECTED). A terminal devicein the idle mode may transition to connected mode, for example becauseit needs to transmit uplink data or respond to a paging request, byundertaking a random access procedure. The random access procedureinvolves the terminal device transmitting a preamble on a physicalrandom access channel and so the procedure is commonly referred to as aRACH or PRACH procedure/process.

In addition to a terminal device deciding itself to initiate a randomaccess procedure to connect to the network, it is also possible for thenetwork, e.g. a base station, to instruct a terminal device in connectedmode to initiate a random access procedure by transmitting to theterminal device an instruction to do so. Such an instruction issometimes referred to as a PDCCH order (Physical Downlink ControlChannel order), see, for example, Section 5.3.3.1.3 in ETSI TS 136 213V13.0.0 (2016 January)/3GPP TS 36.212 version 13.0.0 Release 13 [3].

There are various scenarios in which a network triggered RACH procedure(PDCCH order) may arise. For example:

-   -   a terminal device may receive a PDCCH order to transmit on PRACH        as part of a handover procedure    -   a terminal device that is RRC connected to a base station but        has not exchanged data with the base station for a relatively        long time may receive a PDCCH order to cause the terminal device        to transmit a PRACH preamble so that it can be re-synchronised        to the network and allow the base station to correct timings for        the terminal device    -   a terminal device may receive a PDCCH order so that it can        establish a different RRC configuration in the subsequent RACH        procedure, this may apply, for example, for a narrowband IoT        terminal device which is prevented from RRC reconfiguration in        connected mode whereby sending the terminal device to idle mode        through a PDCCH order allows the terminal device to be        configured in the subsequent PRACH procedure, for example to        configure the terminal device for a different coverage        enhancement level (e.g. more or fewer repetitions)

For convenience, the term PDCCH order is used herein to refer tosignalling transmitted by a base station to instruct a terminal deviceto initiate a PRACH procedure regardless of the cause. However, it willbe appreciated such an instruction may in some cases be transmitted onother channels/in higher layers. For example, in respect of anintra-system handover procedure, what is referred to here as a PDCCHorder may be an RRC Connection Reconfiguration instruction transmittedon a downlink shared channel/PDCCH.

When a PDCCH order is transmitted to a terminal device, the terminaldevice is assigned a PRACH preamble signature sequence to use for thesubsequent PRACH procedure. This is different from a terminal devicetriggered PRACH procedure in which the terminal device selects apreamble from a predefined set and so could by coincidence select thesame preamble as another terminal device PRACHing at the same timegiving rise to potential contention. Consequently, for PRACH proceduresinitiated by a PDCCH order there is less chance for contention withother terminal devices undertaking PRACH procedures at the same timebecause the PRACH preamble for the PDCCH ordered terminal device isscheduled by the network/base station.

FIG. 2 is a ladder diagram schematically showing steps of a conventionalLTE random access procedure undertaken by a terminal device 104(left-hand node in FIG. 2) in response to a PDCCH order received from abase station 101 (right-hand node in FIG. 2). It will be appreciated thespecific reason for undertaking the PDCCH ordered PRACH is notsignificant to the principles described herein.

In step S1 the base station 101 transmits signalling corresponding to aPDCCH order addressed to the terminal device 104. This signallingincludes an indication of a random access preamble signature sequencefor the terminal device to use for the subsequent random accessprocedure. This preamble may be selected by the base station from a poolof preambles that are not available for contention-based (terminaldevice triggered) random access procedures to avoid contention.

In step S2 the terminal device 104 transmits the preamble indicated inassociation with the signalling received in Step S1 on a physical randomaccess channel (PRACH). Based on the radio resources used for the uplinktransmission of the preamble, the terminal device determines a RA-RNTI(Random Access Radio Network Temporary Identity) associated with thetransmission.

In step S3, on receiving the transmission of the random access preamblefrom the terminal device in step S2, the base station 101 transmits aRandom Access Response (RAR) message addressed to the RA-RNTI. The RARmessage contains an indication of the preamble, a timing alignmentcommand and a temporary C-RNTI (Cell Radio Network Temporary Identity)as well as an indication (allocation grant) of uplink resources to beused by the terminal device for the next step of the procedure.

In step S4, assuming the terminal device receives the RAR of step S3from the base station within a specified time window after preambletransmission in step S2, the terminal device transmits a so-calledMessage 3 using the uplink radio resources indicated in association withthe RAR message received in step S3. Message 3 conveys the appropriatehigher-layer message associated with the PRACH procedure. For example,the higher-layer message might be an RRC Connection Resume message, anRRC Connection Reconfiguration Complete message, an RRC ConnectionRe-establishment Request message or an Uplink Information Transfermessage.

For a conventional wireless telecommunications system, Message 3exchanged in step S4 of the processing represented in FIG. 2 wouldnormally be expected to have a fixed size length (if the information tobe conveyed is less than the fixed size, padding is used to provide thefixed size). However, it has been proposed that in some situations itmay be advantageous for Message 3 to have a variable length so that itcan be used by the terminal device to communicate additional informationto that which is normally associated with a conventional Message 3. Thatis to say, it has been proposed that a terminal device may be able to“piggy back” certain data, for example user plane data, on Message 3transmissions of a random access procedure. For example, this may beparticularly advantageous in respect of terminal devices needing totransmit relatively small amounts of data since this data may betransmitted in association with a random access procedure Message 3,thereby saving signalling overhead associated with establishing aseparate uplink transmission for this data.

Accordingly, it is possible that a base station may need to allocatedifferent amounts of uplink radio resources to use for different Message3 transmissions depending on the amount data to be transmitted in theMessage 3. That is to say, in some implementations uplink signallingassociated with a random access procedure may have a variable size. Toaccommodate this it has been proposed that the size of Message 3 beindicated in the random access response, RAR transmitted from the basestation to the terminal device in response to the base station receivingthe random access preamble from the terminal device. However, theinventors have recognised certain drawbacks with this approach. Forexample, RAR messages will be transmitted frequently in wirelesstelecommunication systems, for example in respect of all contention andnon-contention-based random access procedures, and so it would bepreferable for these messages to be as simple and straightforward aspossible, for example it would be preferable to support a single formatfor the RAR message, for both contention and non-contention basedaccess.

FIG. 3 schematically shows a telecommunications system 500 according toan embodiment of the present disclosure. The telecommunications system500 in this example is based broadly around an LTE-type architecture. Assuch many aspects of the operation of the telecommunicationssystem/network 500 are known and understood and are not described herein detail in the interest of brevity. Operational aspects of thetelecommunications system 500 which are not specifically describedherein may be implemented in accordance with any known techniques, forexample according to the current LTE-standards.

The telecommunications system 500 comprises a core network part (evolvedpacket core) 502 coupled to a radio network part. The radio network partcomprises a base station (evolved-nodeB) 504 coupled to a plurality ofterminal devices. In this example, two terminal devices are shown,namely a first terminal device 506 and a second terminal device 508. Itwill of course be appreciated that in practice the radio network partmay comprise a plurality of base stations serving a larger number ofterminal devices across various communication cells. However, only asingle base station and two terminal devices are shown in FIG. 3 in theinterests of simplicity.

As with a conventional mobile radio network, the terminal devices 506,508 are arranged to communicate data to and from the base station(transceiver station) 504. The base station is in turn communicativelyconnected to a serving gateway, S-GW, (not shown) in the core networkpart which is arranged to perform routing and management of mobilecommunications services to the terminal devices in thetelecommunications system 500 via the base station 504. In order tomaintain mobility management and connectivity, the core network part 502also includes a mobility management entity (not shown) which manages theenhanced packet service, EPS, connections with the terminal devices 506,508 operating in the communications system based on subscriberinformation stored in a home subscriber server, HSS. Other networkcomponents in the core network (also not shown for simplicity) include apolicy charging and resource function, PCRF, and a packet data networkgateway, PDN-GW, which provides a connection from the core network part502 to an external packet data network, for example the Internet. Asnoted above, the operation of the various elements of the communicationssystem 500 shown in FIG. 3 may be broadly conventional apart from wheremodified to provide functionality in accordance with embodiments of thepresent disclosure as discussed herein.

In this example, it is assumed the first terminal device 506 is aconventional smartphone-type terminal device communicating with the basestation 504 in a conventional manner. This conventional terminal device506 comprises a transceiver unit 506 a for transmission and reception ofwireless signals and a processor unit 506 b configured to control thedevice 506. The processor unit 506 b may comprise a processor unit whichis suitably configured/programmed to provide the desired functionalityusing conventional programming/configuration techniques for equipment inwireless telecommunications systems. The transceiver unit 506 a and theprocessor unit 506 b are schematically shown in FIG. 3 as separateelements. However, it will be appreciated that the functionality ofthese units can be provided in various different ways, for example usinga single suitably programmed general purpose computer, or suitablyconfigured application-specific integrated circuit(s)/circuitry. As willbe appreciated the conventional terminal device 506 will in generalcomprise various other elements associated with its operatingfunctionality.

In this example, it is assumed the second terminal device 508 is amachine-type communication (MTC) terminal device 508 adapted to supportoperations in an Internet of Things (IoT) context in accordance withembodiments of the present disclosure when communicating with the basestations 504. In this regard, the terminal device 508 may be a reducedcapability terminal device, for example a terminal device able tooperate on a restricted bandwidth as compared to conventional terminaldevices (i.e. what might be referred to as a narrowband device).However, it will be appreciated this represents merely one specificimplementation of approaches in accordance with embodiments of thedisclosure, and in other cases, the same principles may be applied inrespect of terminal devices which are not reduced capability terminaldevices, but may comprise conventional smartphone terminal devices, orindeed any other form of terminal device, that may be operating in awireless telecommunications system (e.g. the smartphone terminal device506 may in other cases also implement the functionality described hereinfor the reduced-capability terminal device 508 in accordance withembodiments of the disclosure).

The IoT terminal device 508 comprises a transceiver unit 508A fortransmission and reception of wireless signals and a processor unit 508Bconfigured to control the terminal device 508. The processor unit 508Bmay comprise various sub-units for providing functionality in accordancewith embodiments of the present disclosure as explained further herein.These sub-units may be implemented as discrete hardware elements or asappropriately configured functions of the processor unit. Thus theprocessor unit 508B may comprise a processor unit which is suitablyconfigured/programmed to provide the desired functionality describedherein using conventional programming configuration techniques forequipment in wireless telecommunications systems. The transceiver unit508A and the processor unit 508B are schematically shown in FIG. 3 asseparate elements for ease of representation. However, it will beappreciated that the functionality of these units can be provided invarious different ways, for example using a single suitably programmedgeneral purpose computer, or suitably configured application-specificintegrated circuit(s)/circuitry. It will be appreciated the terminaldevice 508 will in general comprise various other elements associatedwith its operating functionality, for example a power source, userinterface, and so forth, but these are not shown in FIG. 2 in theinterests of simplicity.

The base station 504 comprises a transceiver unit 504 a for transmissionand reception of wireless signals and a processor unit 504 b configuredto control the base station 504 to operate in accordance withembodiments of the present disclosure as described herein. The processorunit 506 b may again comprise various sub-units, such as a schedulingunit, for providing functionality in accordance with embodiments of thepresent disclosure as explained further below. These sub-units may beimplemented as discrete hardware elements or as appropriately configuredfunctions of the processor unit. Thus, the processor unit 504 b maycomprise a processor unit which is suitably configured programmed toprovide the desired functionality described herein using conventionalprogramming/configuration techniques for equipment in wirelesstelecommunications systems. The transceiver unit 504 a and the processorunit 504 b are schematically shown in FIG. 3 as separate elements forease of representation. However, it will be appreciated that thefunctionality of these units can be provided in various different ways,for example using a single suitably programmed general purpose computer,or suitably configured application-specific integrated circuit(s)circuitry. It will be appreciated the base station 504 will in generalcomprise various other elements associated with its operatingfunctionality.

Thus, the base station 504 is configured to communicate data with boththe conventional smartphone terminal device 506 and the IoT terminaldevice 508 according to an embodiment of the disclosure over respectivecommunication links 510, 512. The base station 504 is configured tocommunicate with the conventional terminal device 506 over theassociated radio communication link 510 following the establishedprinciples of LTE-based communications, and in particular usingconventional random access procedures such as represented in FIG. 2.However, communications between the base station 504 and the IoTterminal device 508 operate using modified random access procedures inaccordance with certain embodiments of the present disclosure asdescribed herein. Thus, one aspect of certain embodiments of thedisclosure is that the base station is configured to operate bycommunicating with different classes of terminal device (e.g. a firstclass of terminal device, for example comprising conventional LTEterminal devices, such as smartphones, and a second class of terminaldevice, for example comprising IoT-type terminal devices) usingdifferent random access procedures. That is to say, a base station mayoperate to communicate with a first class (group/type) of terminaldevice using a first random access procedure (e.g. in accordance withconventional and established random access procedures) and tocommunicate with a second class (group/type) of terminal device using amodified random access procedure, such as described herein. Whether ornot a particular terminal device or base station supports modifiedrandom access procedures in accordance with embodiments of the presentdisclosure may be established in accordance with conventional techniquesfor sharing terminal device and base station capability information inwireless telecommunications networks, for example based on signallingexchange during a RRC connection establishment procedure or based on theability of a terminal device to decode a particular synchronisationsignal or system information message. However, it will be appreciatedthat while in some implementations modified random access procedures maybe used in respect of only certain types of terminal device, in otherimplementations the same modified procedures may be used in a wirelesstelecommunications system in respect of all terminal devices.

FIG. 4 is a ladder diagram schematically showing steps of a modifiedrandom access procedure undertaken by the terminal device 508 (left-handnode in FIG. 4) and the base station 504 (right-hand node in FIG. 4)represented in FIG. 3 in accordance with certain embodiments of thedisclosure. As already mentioned, it will be appreciated aspects of thisoperation which are not specifically described herein, for example theparticular signalling protocols adopted, may be implemented inaccordance with conventional techniques for communicating in wirelesstelecommunications systems. It will further be appreciated the processof FIG. 4 is closely based on the conventional process of FIG. 2 andaspects of FIG. 4 which correspond with aspects of FIG. 2 are notdiscussed in detail in the interests of brevity.

In step T1 of the signalling represented in FIG. 4 it is assumed theterminal device 508 is operating in an RRC connected mode with respectto the base station 504 in accordance with conventional techniques. Itwill be appreciated the reason why the terminal device is RRC connectedto the base station and the contents of any data being exchanged betweenthe terminal device and the base station is not significant to theprinciples described herein.

In step T2 the base station 504 identifies a need to trigger theterminal device 508 to undergo a random access procedure. The specificreason why the base station determines the terminal device shouldundergo a random access procedure is not significant to the principlesdescribed herein. However, for the sake of a concrete example, it isassumed here the terminal device is unable to reconfigure its RRCconnection whilst RRC connected, for example as has been suggested forIoT type terminal devices, but the base station determines the currentRRC configuration settings for the terminal device are not appropriate.For example, the base station may recognise the terminal device needs tobe reconfigured to change its coverage enhancement settings, for exampleby increasing the number of repetitions associated with coverageenhancement functions applied for the terminal device. This may be thecase, for example, because the base station recognises the current RRCconfiguration does not provide sufficient coverage enhancement to allowfor the reliable exchange of data between the base station and theterminal device.

In step T3, the base station determines an amount of data for theterminal device to transmit to the base station in association withuplink signalling for the random access procedure that will result fromstep T2. That is to say, the random access procedure is configured toallow for a variable size message 3, and prior to triggering the randomaccess procedure, the base station determines a length/size (i.e. atransport block size, TBS) of a message 3 uplink transmission associatedwith the yet-to-be triggered random access procedure. For example, thebase station may be aware of how much uplink data is being buffered bythe terminal device from buffer status information received from theterminal device in association with step T1. The base station may thusbe aware that the terminal device has N bits of uplink data to transmit,and decides the amount of this data that should be transmitted by theterminal device in uplink signalling associated with the random accessprocedure. The actual amount of data to be transmitted by the terminaldevice in the PRACH procedure, e.g. the TBS for message 3, may bedetermined by the base station in step T3 having regard to the generallyestablished principles for scheduling transmissions in wirelesstelecommunication systems.

In step T4 the base station 504 transmits signalling to the terminaldevice 508 to instruct the terminal device to initiate a PRACHprocedure. This signalling may be based on a conventional PDCCH order,for example as discussed above with reference to step S1 of FIG. 2, butmodified to additionally provide the terminal device with an indicationof the amount of data for the terminal device to transmit to the basestation in uplink signalling associated with the random accessprocedure. That is to say, the signalling of step T4 may provide theterminal device 508 with an indication of a transport block size (asdetermined by the base station in step T3) to be used for message 3 inthe random access procedure triggered by the signalling of step T4. Forexample, the indication of the transport block size to use for Message 3could be conveyed in a bit field within the Downlink Control Information(DCI) carried by the PDCCH. There are various different ways in whichthe base station may convey an indication of the transport block size tobe used in association with random access procedure uplink signalling,as discussed further below. It will be appreciated that whilst thesignalling of step T4 may in some cases correspond with a modified PDCCHorder, in other implementations different forms of signalling may beadopted, for example the information conveyed in step T4 of FIG. 4 maybe conveyed by higher layer signalling, such as an RRC message.

In step T5 the terminal device 508 responds to the instruction toinitiate a random access procedure received in step T4 by initiating therandom access procedure through transmission of a random access preambleto the base station. This step may be performed in accordance withconventional random access procedures, for example the step maycorrespond with step S2 discussed above with reference to FIG. 2.Accordingly, and as is conventional, the random access preamblesignature sequence used by the terminal device for the transmission instep T5 may be based on an indication received from the base station inassociation with the instruction to initiate the random access procedurereceived in step T4 to help avoid contention.

In step T6, after receiving the random access preamble from the terminaldevice in step T5, the station responds with a random access responsemessage (RAR). The RAR may be conventional, for example, and correspondwith the random access response message discussed above in relation tostep S3 of FIG. 2.

In step T7, on receiving the RAR message of step T6, the terminal deviceproceeds to transmit a random access procedure message 3 with atransport block size corresponding to the size indicated in thesignalling received from the base station providing an instruction totrigger the random access procedure in step T4. The actual datatransmitted by the terminal device in this variable size message 3 willdepend on the implementation at hand and is not significant to theprinciples described herein. For example, the terminal device maytransmit an amount of user plane data in its uplink buffer inconjunction with an otherwise conventional random access message 3,wherein the amount of data transmitted is based on the indicatedtransport block size received from the base station in the instructionto initiate the random access procedure in step T4.

Thus, in accordance with the principles described above, a variable sizemessage 3 can be used to allow a terminal device to transmit differentamounts of data in uplink signalling associated with a random accessprocedure, and furthermore, this is achieved in a way which does notrequire a modified random access response message. Instead, the terminaldevice is provided with an indication of the transport block size forthe uplink signalling associated with the random access procedure (inthis example message 3 signalling) in conjunction with a previouslyreceived instruction to initiate a random access procedure received fromthe base station (step T4 in this example). This can simplify RARdecoding and reduce the number of bits that need to be transmitted inRAR messages.

As noted above there are various different ways in which the basestation 504 may provide the terminal device 508 with an indication ofthe size, e.g. TBS, for subsequent uplink signalling associated with arandom access procedure, e.g. a message 3, in association with aninstruction for the terminal device to initiate a random accessprocedure, e.g. a PDCCH order or higher layer signalling.

As already discussed, the base station may in association with thetrigger instruction to initiate the random access procedure (step T4 inthe example of FIG. 4) also provide the terminal device with anindication of the random access preamble to use for the random accessprocedure. This is an established principle for network triggered(non-contention) random access procedures in wireless telecommunicationssystems. However, in accordance with certain embodiments of the presentdisclosure, the specific preamble chosen by the base station for theterminal device to use in the PRACH procedure may be used to provide anindication of a subsequent uplink message size. For example, in a simpleimplementation the wireless telecommunications system may allow twodifferent sizes for message 3. In this case the preambles available fornon-contention random access procedures may be divided into two groups,with one group associated with one length for message 3 and the othergroup associated with another length for message 3. The base station cantherefore select from one or other group to provide the terminal devicewith an indication of the size of message 3 it should use in thesubsequent random access procedure. Of course in any givenimplementation there may be more than two different message 3 sizesavailable, and correspondingly more than two predefined groups of randomaccess preambles. The predefined associations between differentpreambles and message sizes may be provided in accordance with anoperating standard for the wireless telecommunications systems, or maybe configurable, for example through system information signalling. Itmay be noted in some scenarios for a contention based random accessprocedure a terminal device may itself be configured to select apreamble to provide an indication of an intended message 3 size based ona predefined association between different message 3 sizes and differentpreambles/preamble groups available for selection by the terminal devicefor contention-based random access.

In other examples the transport block size for the terminal device touse for subsequent uplink signalling associated with the random accessprocedure may be explicitly indicated in association with the signallingreceived from the base station to trigger the terminal device toinitiate the random access procedure. For example, referring to FIG. 4,the signalling of step T4 may be associated with an explicit indicationof the TBS to use. The explicit indication of the TBS could betransmitted within an information element of an RRC message or a bitfield of Downlink Control Information (DCI) transmitted on a PDCCH.

In other examples a context/cause associated with the signalling totrigger PRACH (e.g. the PDCCH order) may implicitly indicate thetransport block size to be used for message 3 in the PRACH procedure.For example, in accordance with a predefined association, an instructionto initiate a random access procedure in association with a handoveroperation may correspond with one TBS size, an instruction to initiate arandom access procedure to achieve re-synchronisation may be associatedwith another TBS size, and an instruction to initiate a random accessprocedure to achieve an RRC reconfiguration may be associated with yetanother TBS size. A terminal device may be able to in effect determinethe context of a PDCCH order from previous signalling characteristics.E.g. if the terminal device recognizes it has not had reliablecommunications during a preceding period, it may assume a PDCCH order isto reconfigure the device for a different repetition rate. If theterminal device recognizes it has not received downlink signalling forsome time, it may assume a PDCCH order is to achieve resynchronisation.

In other examples the content of the instruction to initiate a randomaccess procedure (e.g. a PDCCH order or higher-layer instruction) mayprovide an indication of the transport block size to use for subsequentuplink signalling associated with the random access procedure (e.g. amessage 3 in an LTE context). For example, in the case of the randomaccess trigger instruction from the base station being issued to allowfor RRC reconfiguration, different RRC configurations may be associatedwith different message 3 sizes. Accordingly, the base station mayprovide an indication of a RRC configuration to be adopted inassociation with the signalling to trigger the terminal device toinitiate the random access procedure, and this may indicate a particularmessage size for subsequent uplink signalling associated with the randomaccess procedure in accordance with a predefined association/mapping.

Thus there has been described a method of operating a terminal device ina wireless telecommunications network comprising the terminal device anda base station. The wireless telecommunications network supports arandom access procedure comprising an exchange of random accessprocedure messages between the terminal device and the base station. Atleast one of the random access procedure messages is a variable sizeuplink message. The method comprises: receiving from the base station aninstruction to perform the random access procedure, wherein theinstruction to perform the random access procedure is conveyed inassociation with an indication of a message size to be used by theterminal device for the variable size uplink message during the randomaccess procedure; and performing the random access procedure byexchanging random access procedure messages with the base station,including transmitting the uplink message of variable size with a sizecorresponding to the indicated message size received from the basestation.

It will be appreciated that the principles described herein are notapplicable only to certain types of terminal device, but can be appliedmore generally in respect of any types of terminal device, for examplethe approaches are not limited to machine type communication devices/IoTdevices or other narrowband terminal devices, but can be applied moregenerally, for example in respect of any type terminal device operatingwith a wireless link to the communication network.

Further particular and preferred aspects of the present invention areset out in the accompanying independent and dependent claims. It will beappreciated that features of the dependent claims may be combined withfeatures of the independent claims in combinations other than thoseexplicitly set out in the claims.

It will further be appreciated that the principles described herein arenot applicable only to LTE-based wireless telecommunications systems,but are applicable for any type of wireless telecommunications systemthat supports a random access procedure comprising an exchange of randomaccess procedure messages between a terminal device and a base stationwhere at least one of the random access procedure messages is a variablesize uplink message.

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting of the scopeof the invention, as well as other claims. The disclosure, including anyreadily discernible variants of the teachings herein, define, in part,the scope of the foregoing claim terminology such that no inventivesubject matter is dedicated to the public.

Respective features of the present disclosure are defined by thefollowing numbered paragraphs:

1. A method of operating a terminal device in a wirelesstelecommunications network comprising the terminal device and a basestation, wherein the wireless telecommunications network supports arandom access procedure comprising an exchange of random accessprocedure messages between the terminal device and the base station,wherein at least one of the random access procedure messages is avariable size uplink message; wherein the method comprises:

-   -   receiving from the base station an instruction to perform the        random access procedure, wherein the instruction to perform the        random access procedure comprises an indication of a message        size to be used by the terminal device for the variable size        uplink message during the random access procedure; and    -   performing the random access procedure by exchanging random        access procedure messages with the base station, including        transmitting the uplink message of variable size with a size        corresponding to the indicated message size received from the        base station.

2. The method of paragraph 1, wherein the indication of the message sizeto be used by the terminal device for the variable size uplink messageis conveyed explicitly in information received from the base station inassociation with the instruction to perform the random access procedure.

3. The method of paragraph 1, wherein the instruction to perform therandom access procedure is associated with an indication of a randomaccess preamble signature sequence to be used by the terminal device inan uplink message to initiate the random access procedure, and whereinthe indication of the message size to be used by the terminal device forthe variable size uplink message is conveyed implicitly by the indicatedrandom access preamble signature sequence, whereby different randomaccess preamble signature sequences correspond with different sizes forthe variable size message in accordance with a predefined association.

4. The method of paragraph 1, wherein the indication of the message sizeto be used by the terminal device for the variable size uplink messageis conveyed implicitly by a context for performing the random accessprocedure, whereby different contexts for performing the random accessprocedure correspond with different sizes for the variable size messagein accordance with a predefined association.

5. The method of paragraph 1, wherein the indication of the message sizeto be used by the terminal device for the variable size uplink messageis conveyed implicitly by information content included in theinstruction to perform the random access procedure to convey otherinformation, whereby different information contents for the otherinformation correspond with different sizes for the variable sizemessage in accordance with a predefined association.

6. The method of paragraph 1, wherein the information content includedin the instruction to perform the random access procedure to conveyother information comprises an indication of a radio resource controlconfiguration for the terminal device, whereby different radio resourcecontrol configurations correspond with different sizes for the variablesize message in accordance with a predefined association.

7. The method of any of paragraphs 1 to 6, wherein the random accessprocedure messages comprise at least a first message, a second message,and a third message, wherein the first message comprises an uplinkmessage conveying a random access preamble signature sequence from theterminal device to the base station to initiate the random accessprocedure, the second message is a downlink message transmitted inresponse to the first message and conveying an indication of anallocation of uplink radio resources to be used by the terminal fortransmitting the third message, and the third message is thevariable-size uplink message.

8. The method of any of paragraphs 1 to 7, wherein the indication of amessage size to be used by the terminal device for the variable sizeuplink message during the random access procedure comprises anindication of a transport block size, TBS, to be used for the variablesize uplink message during the random access procedure.

9. The method of any of paragraphs 1 to 8, wherein the instruction toinitiate a random access procedure is received from the base stationwhile the terminal device is in a radio resource control connected modeof operation with respect to the base station.

10. The method of any of paragraphs 1 to 9, wherein the instruction toinitiate a random access procedure comprises a physical downlink controlchannel, PDCCH, order.

11. A terminal device for use in a wireless telecommunications networkcomprising the terminal device and a base station, wherein the wirelesstelecommunications network supports a random access procedure comprisingan exchange of random access procedure messages between the terminaldevice and the base station, wherein at least one of the random accessprocedure messages is a variable size uplink message; wherein theterminal device comprises a controller unit and a transceiver unitconfigured such that the terminal device is operable to:

-   -   receive from the base station an instruction to perform the        random access procedure, wherein the instruction to perform the        random access procedure comprises an indication of a message        size to be used by the terminal device for the variable size        uplink message during the random access procedure; and    -   perform the random access procedure by exchanging random access        procedure messages with the base station, including transmitting        the uplink message of variable size with a size corresponding to        the indicated message size received from the base station.

12. Integrated circuitry for a terminal device for use in a wirelesstelecommunications network comprising the terminal device and a basestation, wherein the wireless telecommunications network supports arandom access procedure comprising an exchange of random accessprocedure messages between the terminal device and the base station,wherein at least one of the random access procedure messages is avariable size uplink message, wherein the integrated circuitry comprisesa controller element and a transceiver element configured to operatetogether such that the terminal device is operable to:

-   -   receive from the base station an instruction to perform the        random access procedure, wherein the instruction to perform the        random access procedure comprises an indication of a message        size to be used by the terminal device for the variable size        uplink message during the random access procedure; and    -   perform the random access procedure by exchanging random access        procedure messages with the base station, including transmitting        the uplink message of variable size with a size corresponding to        the indicated message size received from the base station.

13. A method of operating a base station in a wirelesstelecommunications network comprising the base station and a terminaldevice, wherein the wireless telecommunications network supports arandom access procedure comprising an exchange of random accessprocedure messages between the terminal device and the base station,wherein at least one of the random access procedure messages is avariable size uplink message; wherein the method comprises:

-   -   transmitting to the terminal device an instruction to perform        the random access procedure, wherein the instruction to perform        the random access procedure comprises an indication of a message        size to be used by the terminal device for the variable size        uplink message during the random access procedure; and    -   engaging in the random access procedure for the terminal device        by exchanging random access procedure messages with the terminal        device, including receiving the uplink message of variable size        with a size corresponding to the indicated message size        transmitted to the terminal device.

14. A base station for use in a wireless telecommunications networkcomprising the base station and a terminal device, wherein the wirelesstelecommunications network supports a random access procedure comprisingan exchange of random access procedure messages between the terminaldevice and the base station, wherein at least one of the random accessprocedure messages is a variable size uplink message, wherein the basestation comprises a controller unit and a transceiver unit configuredsuch that the base station is operable to:

-   -   transmit to the terminal device an instruction to perform the        random access procedure, wherein the instruction to perform the        random access procedure comprises an indication of a message        size to be used by the terminal device for the variable size        uplink message during the random access procedure; and    -   engage in the random access procedure for the terminal device by        exchanging random access procedure messages with the terminal        device, including receiving the uplink message of variable size        with a size corresponding to the indicated message size        transmitted to the terminal device.

15. Integrated circuitry for a base station for use in a wirelesstelecommunications network comprising the base station and a terminaldevice, wherein the wireless telecommunications network supports arandom access procedure comprising an exchange of random accessprocedure messages between the terminal device and the base station,wherein at least one of the random access procedure messages is avariable size uplink message, wherein the integrated circuitry comprisesa controller element and a transceiver element configured to operatetogether such that the base station is operable to:

-   -   transmit to the terminal device an instruction to perform the        random access procedure, wherein the instruction to perform the        random access procedure comprises an indication of a message        size to be used by the terminal device for the variable size        uplink message during the random access procedure; and    -   engage in the random access procedure for the terminal device by        exchanging random access procedure messages with the terminal        device, including receiving the uplink message of variable size        with a size corresponding to the indicated message size        transmitted to the terminal device.

REFERENCES

[1] ETSI TS 122 368 V12.4.0 (2014 October)/3GPP TS 22.368 version 12.4.0Release 12

[2] Holma H. and Toskala A, “LTE for UMTS OFDMA and SC-FDMA based radioaccess”, John Wiley and Sons, 2009

[3] ETSI TS 136 213 V13.0.0 (2016 January)/3GPP TS 36.212 version 13.0.0Release 13

1. A method of operating a terminal device in a wirelesstelecommunications network comprising the terminal device and a basestation, wherein the wireless telecommunications network supports arandom access procedure comprising an exchange of random accessprocedure messages between the terminal device and the base station,wherein at least one of the random access procedure messages is avariable size uplink message; wherein the method comprises: receivingfrom the base station an instruction to perform the random accessprocedure, wherein the instruction to perform the random accessprocedure comprises an indication of a message size to be used by theterminal device for the variable size uplink message during the randomaccess procedure; and performing the random access procedure byexchanging random access procedure messages with the base station,including transmitting the uplink message of variable size with a sizecorresponding to the indicated message size received from the basestation.
 2. The method of claim 1, wherein the indication of the messagesize to be used by the terminal device for the variable size uplinkmessage is conveyed explicitly in information received from the basestation in association with the instruction to perform the random accessprocedure.
 3. The method of claim 1, wherein the instruction to performthe random access procedure is associated with an indication of a randomaccess preamble signature sequence to be used by the terminal device inan uplink message to initiate the random access procedure, and whereinthe indication of the message size to be used by the terminal device forthe variable size uplink message is conveyed implicitly by the indicatedrandom access preamble signature sequence, whereby different randomaccess preamble signature sequences correspond with different sizes forthe variable size message in accordance with a predefined association.4. The method of claim 1, wherein the indication of the message size tobe used by the terminal device for the variable size uplink message isconveyed implicitly by a context for performing the random accessprocedure, whereby different contexts for performing the random accessprocedure correspond with different sizes for the variable size messagein accordance with a predefined association.
 5. The method of claim 1,wherein the indication of the message size to be used by the terminaldevice for the variable size uplink message is conveyed implicitly byinformation content included in the instruction to perform the randomaccess procedure to convey other information, whereby differentinformation contents for the other information correspond with differentsizes for the variable size message in accordance with a predefinedassociation.
 6. The method of claim 1, wherein the information contentincluded in the instruction to perform the random access procedure toconvey other information comprises an indication of a radio resourcecontrol configuration for the terminal device, whereby different radioresource control configurations correspond with different sizes for thevariable size message in accordance with a predefined association. 7.The method of claim 1, wherein the random access procedure messagescomprise at least a first message, a second message, and a thirdmessage, wherein the first message comprises an uplink message conveyinga random access preamble signature sequence from the terminal device tothe base station to initiate the random access procedure, the secondmessage is a downlink message transmitted in response to the firstmessage and conveying an indication of an allocation of uplink radioresources to be used by the terminal for transmitting the third message,and the third message is the variable-size uplink message.
 8. The methodof claim 1, wherein the indication of a message size to be used by theterminal device for the variable size uplink message during the randomaccess procedure comprises an indication of a transport block size, TBS,to be used for the variable size uplink message during the random accessprocedure.
 9. The method of claim 1, wherein the instruction to initiatea random access procedure is received from the base station while theterminal device is in a radio resource control connected mode ofoperation with respect to the base station.
 10. The method of claim 1,wherein the instruction to initiate a random access procedure comprisesa physical downlink control channel, PDCCH, order.
 11. A terminal devicefor use in a wireless telecommunications network comprising the terminaldevice and a base station, wherein the wireless telecommunicationsnetwork supports a random access procedure comprising an exchange ofrandom access procedure messages between the terminal device and thebase station, wherein at least one of the random access proceduremessages is a variable size uplink message; wherein the terminal devicecomprises a controller unit and a transceiver unit configured such thatthe terminal device is operable to: receive from the base station aninstruction to perform the random access procedure, wherein theinstruction to perform the random access procedure comprises anindication of a message size to be used by the terminal device for thevariable size uplink message during the random access procedure; andperform the random access procedure by exchanging random accessprocedure messages with the base station, including transmitting theuplink message of variable size with a size corresponding to theindicated message size received from the base station.
 12. Integratedcircuitry for a terminal device for use in a wireless telecommunicationsnetwork comprising the terminal device and a base station, wherein thewireless telecommunications network supports a random access procedurecomprising an exchange of random access procedure messages between theterminal device and the base station, wherein at least one of the randomaccess procedure messages is a variable size uplink message, wherein theintegrated circuitry comprises a controller element and a transceiverelement configured to operate together such that the terminal device isoperable to: receive from the base station an instruction to perform therandom access procedure, wherein the instruction to perform the randomaccess procedure comprises an indication of a message size to be used bythe terminal device for the variable size uplink message during therandom access procedure; and perform the random access procedure byexchanging random access procedure messages with the base stationincluding transmitting the uplink message of variable size with a sizecorresponding to the indicated message size received from the basestation. 13-14. (canceled)
 15. Integrated circuitry for a base stationfor use in a wireless telecommunications network comprising the basestation and a terminal device, wherein the wireless telecommunicationsnetwork supports a random access procedure comprising an exchange ofrandom access procedure messages between the terminal device and thebase station, wherein at least one of the random access proceduremessages is a variable size uplink message, wherein the integratedcircuitry comprises a controller element and a transceiver elementconfigured to operate together such that the base station is operableto: transmit to the terminal device an instruction to perform the randomaccess procedure, wherein the instruction to perform the random accessprocedure comprises an indication of a message size to be used by theterminal device for the variable size uplink message during the randomaccess procedure; and engage in the random access procedure for theterminal device by exchanging random access procedure messages with theterminal device, including receiving the uplink message of variable sizewith a size corresponding to the indicated message size transmitted tothe terminal device.